Submarine cable coupling with impedance matching means



July 8, 1969 R LANGMACK ET AL 3,454,707

SUBMARINE CABLE COUPLING WITH IMPEDANCE MATCHING MEANS R. M. LANGMACKlNl/ENTORS J.n. PHELPS 0. P. wooomo M QM ATTORNEY Sheet Filed Oct. 30,1967 J y 1969 R. M. LANGMACK ET' AL 3,454,707

SUBMARINE CABLE COUPLING WITH IMPEDANCE MATCHING MEANS Filed Oct. 50.1967 Sheet 2 of z i m i :v lg,

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United States Patent U.S. Cl. 174-70 7 Claims ABSTRACT OF THE DISCLOSUREA flexible undersea coupling between a submarine coaxial cable and arepeater employs a gimbaled tension transfer member that maintains animpedance match between the cable and repeater. The structure primarilyemployed is metallic cone for anchoring the inner cable conductor, aceramic bulk aflixed to the cone and a polyethylene envelope cast aroundthe cone and the ceramic.

This invention relates to coaxial cable couplings and more specificallyto an underwater cable coupling for connecting armorless cable to itsrepeaters without introducing impedance mismatch.

Background of the invention In underwater cable systems, couplings arethe electrical and mechanical interface between the cable proper and oneend of a repeater. Broadly, their function is two-fold: to mechanicallylink the cable strength member firmly to the repeater; and toelectrically connect the conductive and dielectric portions of the cablewith the repeater. In practice, these functions often are performedconcurrently by the same structural members. In past coupling designshowever, an optimal mechanical link has been a less than satisfactoryelectrical connection in important respects.

One problem characteristic of previous couplings was the impedancemismatch between coupling and repeater, introduced by the mechanicalrequirements of tension transfer between cable strength member andcoupling. The mismatch has been remedied by adding compensating networksto each repeater, which increase the cost of the system while decreasingits reliability. A solution to the problem at its source, however, hasbeen elusive for want of a sturdy tension transfer member whosemechanical design measures the same impedance-wise as the repeater.

Hence, one primary object of the invention is to balance the impedanceof a cable coupling and the associated repeater.

A more specific object of the invention is to eifect a strong mechanicaltie between cable and coupling without introducing an impedanceimbalance between the coupling and its repeater.

Summary of the inventive conc pt These and other objects are achievedpursuant to the invention by a cable coupling having as a key element atension transfer member comprising a ceramic anchor engaged on a strandtermination cone and imbedded in a polyethylene body, the anchors outerface running at all points substantially parallel to the dielectricfield associated with the polyethylene.

The cone itself is a product of extensive shape optimization geared toaccommodate the strength strands in the least possible volume and toprovide further an engaging surface for the ceramic anchor.Additionally, the gimbals associated with the tension member are locatedsubice stantially in the same plane as the coaxial pigtail whichelectrically connects the strength member to the repeater. Thus, lessflexural strength is required at the pigtail.

Features of the invention, accordingly, include but are not limited to:

An improved tension transfer member characterized by a ceramic anchorwhose outer face and the coming polyethylene coincide in a plane that isessentially parallel to the dielectric field;

An improved strand termination cone; and

An improved relationship between the gimbaling and the coaxial pigtail.

Detailed description. of the drawing FIG. 1 is a side perspective viewshowing in breakaway the several elements of the coupling; and

FIG. 2 is a side view of the anchor molding assembly.

Detailed description of an. illustrative embodiment FIG. 1 illustratesan ocean cable coupling, designated 10, in which the inventive conceptsare embodied. Coupling 10 is equipped for bolting to a repeater endsurface through its gimbal housing 11. Gimbal ring 12 is engaged throughtwo gimbal pins 13 (one shown) to housing 11. Gimbaled to ring 12through two pins 14 (one shown) is a cone housing cap 15. Cap 15 in turnis threaded to cone housing 16.

The ocean cable to be accommodated in coupling 10, and designated 20,"isof the coaxial type comprising an inner stranded steel wire 21surrounded by a metallic jacket 22, the two respectively comprising thestrength member and the cable inner conductor. A solid dielectric core23, normally polyethylene, surrounds jacket 22.

,1 Around dielectric core 23 is the outer conductor 24 of the coaxialcable. Conductor 24 is a copper tube electrically secured to thecoupling between the end of housing 16 and the shoulder of a collar 25which threads to housing 16. This joint is further secured by a ring 26.Cable 20 is provided with an outer jacket 27, also normally ofpolyethylene, which surrounds outer conductor 24 In the final couplingassembly shown in FIG. 1 the polyethylene core 23 is continuous fromcable 20, through an anchor molding assembly 40, and on into thedielectric of a pigtail lead 52 to the repeater. The structure whichachieves this continuity is shown in FIG. 2 and will be describedshortly.

A boot frame 28 is embedded within a heavy rubber boot 29 and isthreaded to collar 25. The rubber boat 29 limits the flexing of cable 20at the coupling. A bellows 30 made of rubber or the like is secured atone end by strap 31 to a flange of frame 28 and at the other end bystrap 32 to a flange of gimbal housing 11. Bellows 30 protects theinside of coupling 10 while allowing the gimbaling movement to occur.Within the boot assembly 28 and 29, outer conductor 24- is covered andprotected by a spacer 35 of the same material as jacket 27 that iswelded into place with the jacket, and extends to ring 26. A tube ofirradiated polyethylene 34 is heat shrunk to a snug fit over collar 25,spacer 35 and jacket 27 to protect the structure during part of theassembly operation.

FIG. 2 shows the anchor molding assembly 40. Strength strand 21 isspread and anchored, as with epoxy, to the interior core of atermination cone 41. Cone 41 advantageously is constructed of berylliumcopper. Its interior surface is optimally designed to effect thegreatest possiblesecuring strength in the least possible space. Thisinterior design is characterized by a small amount of flare, as in whatis known as a bell shape, of a particular exponential curvature, whichassures an essentially uniform decrease in tension in the several wiresfrom the cable end to the coupling end.

Cone 41 includes a forward flange 42 rising from its exterior surface asshOWn in FIG. 2. To this exterior surface a dielectric anchor 43 made ofcertain qualities of ceramic or the like is engaged. Anchor 43 has atapered interior which fits the taper of the exterior of cone 41. Theforward end of anchor 43 is beveled to engage flange 42 of cone 41.Anchor 43 comprises a forward conical surface 44 and a rear conicalsurface 45. Ceramics suitable for constructing anchor 43 includealuminum oxide in one embodiment although other constituents such asberyllium oxide could be used.

Assembly 40 also includes a cone fill tube 46 secured to the nose ofcone 41 and through which epoxy or the like is introduced for anchoringthe strands 21. Tube 46 also provides electrical connection between cone41 and the repeater in well-known fashion. A cone extension tube 47leads out the interior rear entrance to cone 41 and envelops the innerconductor 22 to provide inner conductor electrical continuity.

Assembly 40 also includes a polyethylene molding 48 as shown in FIG. 2,which surrounds anchor 43. Molding 48 has an outer surface which is inflush contact with the inner surface of housing 16 and also in flushcontact with the inner surface of cap when it is threaded to housing 16.It is in this region of the inventive structure that the desiredimpedance balance is achieved, pursuant to the invention, by maintainingan essentially constant level of capacitance between the outer metalliccap 15 and housing 16, and the inner cone 41.

More specifically, a certain capacitance level exists between jacket 22(the inner conductor of the cable) and cable outer conductor 24.Similarly, at any cross section taken through anchor 43 and assembly 40,the capacitance between the metallic members must be the same. Thechoice of the dielectric materials (polyethylene and certain ceramics inthe instant embodiment) as well as the relative cross sections of themetallic cap 15, housing 16 and cone 41 are the critical parameters tobe balanced, given the basic guides of a constant capacitive level, anda taper for load handling purposes to both the ceramic anchor 43 and themolding 48. The configuration shown in FIGS. 1 and 2 is believedoptimal.

Molding 48 also is the agent for transfer of load between the rearsurface 45 of anchor 43 and the cone hous ing 16. Specifically, loadfrom ocean cable is imparted to termination cone 41 through strands 21;thence to anchor 43 and polyethylene molding 48.

Dielectric continuity is afforded from cable dielectric 23 to the tailend 49 of molding 48 by a process of hot molding, after strands 21 areassembled to assembly 40 and the latter is encased in cone housing 16and cap 15 and inner conductor continuity is achieved by connection ofcone extension tube 47 and conductor 22 by welding or brazing.Similarly, dielectric continuity is provided between the front end 50 ofmolding 48 and the dielectric 52 of the repeater connection pigtail by ahot molding process after the pigtail inner conductor 51 has beenattached to cone fill tube 46 by welding or brazing.

Electrical continuity between the outer conductor 24 of cable 20 and theouter conductor 54 of the repeater connection pigtail is effectedthrough cone housing 16, cap 15 and pigtail cap 53 secured to housingcap 15. Of further advantage is the location of said joint between frontend 50 and pigtail dielectric 52 at least partly in the plane of thepoint of intersection of assumed projections from gimbal during thegimbaling and hence is subject to less fatigue jeopardy.

It is to be understood that the embodiments described herein are merelyillustrative of the principles of the invention. Various modificationsmay be made thereto by persons skilled in the art without departing fromthe spirit and scope of the invention.

What is claimed is:

1. A load transfer device between an ocean cable having a centerstrength member and a repeater housing, comprising:

a termination cone receiving said center strength member, said conecomprising conical interior and exterior surfaces and a forward flange;

a dielectric anchor engaged upon said cone exterior surface and abuttingsaid flange, said anchor comprising a truncated conical load-bearingouter surface; and

a polyethylene load-bearing body encapsulating said cone and saidanchor, said body also effecting a dielectric continuum between saidocean cable and said repeater housing,

the outer surface of said anchor running substantially parallel to thedielectric field.

2. A load transfer device in accordance with claim 1 wherein saiddielectric anchor is a ceramic.

3. A coupling between a coaxial cable including a center strength memberand an outer conductor and a repeater, comprising:

means supporting a gimbaled housing;

means for transferring tension between the cable center strength memberand said housing comprising a termination cone including a conicalinterior receiving said strength member, a conical exterior surface, anda forward flange; a dielectric anchor engaged upon said cone exteriorsurface and abutting said flange, said anchor comprising a truncatedrear conical load-bearing surface; and a polyethylene load-bearing bodyencapsulating said cone and said anchor;

means including said polyethylene body for effecting a dielectriccontinuum between said ocean cable and said repeater; and

means including said polyethylene body for effecting electricalconnection between said cable and said repeater.

4. A coupling in accordance with claim 3 wherein the outer surface ofsaid anchor runs substantially parallel at all points to the dielectricfield.

5. A coupling in accordance with claim 4 wherein said dielectric anchoris a ceramic and said termination cone is composed of beryllium copper.

6. A coupling in accordance with claim 5 further comprising meansincluding a metallic pigtail situated at least partly on either side ofthe gimbals of said housing for effecting electrical connection betweenthe outer conductor of said cable and said repeater.

7. A coupling in accordance with claim 6 wherein said electricalconnection means further comprises said gimbaled housing.

FOREIGN PATENTS 1/ 1965 Canada. 9/ 1960 Great Britain.

LARAMIE E. ASKINS, Primary Examiner.

U.S. Cl. X.R.

